The effects of 0.4% and 0.8% Mn element content on the tensile strength and yield strength of highsaturation Al-8Zn-1.8Mg-1.4Cu alloy forgings were investigated by means of transmission electron microscopy

high resolution transmission electron microscopy

room temperature tensile testing and JMatPro software.The results reveal that with 0.4% and 0.8% Mn addition

the tensile strength of the Al-8Zn-1.8Mg-1.4Cu alloy reaches 545 MPa and 553 MPa

respectively

which is increased by 7.9%and 9.5%compared with that of the matrix alloy

and the yield strength reaches 448 MPa and 469 MPa

which is increased by 16.3% and 17.4% compared with that of the matrix alloy.The Al

6

Mn precipitate phase can be formed in the solution heat treatment alloy with the Mn addition after solid solution and ageing treatment

where the Al

6

Mn precipitate phase exists in the shape of a rod inside and outside the grains

and the amounts are increased with the increase of the Mn content.In addition

the precipitated phase of Al

6

Mn exists in a non-coherent form with the aluminum matrix after solution heat treatment

and the strength of the alloy is enhanced by dispersion of Al

6

Mn phases.The Mn atom can replace the Al atom in the aluminum matrix

resulting in the lattice expansion of the face-centered cubic aluminum matrix and the lattice constant increase

so leading to lattice distortion and solid solution strengthening.